MagicTile by Roice Nelson.
This program lets you play Rubik's cube represented thru a Stereographic Projection. It also has lots of other Magic Polyhedron variations, all steographically projected.
Too bad is that the software show only the projected 2D image only, not the actual 3D projection scene.
Home page: http://www.gravitation3d.com/magictile/.
Win

MoebApplet

MoebApplet, by Paul Murray. This Java applet does real-time interactive Mobius transformation. If you are studying Mobius Transformation, this is the best applet for it. You can drag the fixed points, the poles, and a few other critical points in the plane and see the image change as you move.
Home page:
http://www.paulmurray.id.au/Java/MoebApplet.html.
Java

NonEuclid

NonEuclid by Joel Castellanos. It is a free software for drawing hyperbolic geometry. Its function is similar to Geometer's Sketchpad except it is not real-time interactive. Elements cannot be dragged around once drawn. The program comes with a tutorial on hyperbolic geometry.
Home page: http://cs.unm.edu/~joel/NonEuclid/NonEuclid.html.
Java